TWI552716B - Laryngoscope and operation method thereof - Google Patents

Description

Throat mirror and its operation method

The present invention relates to a laryngoscope, and more particularly to a laryngoscope for photography.

The conventional laryngoscope is used by a physician to observe the path of the trachea by using the patient's anatomy to establish a visual guiding route. The photographic laryngoscope provides the glottis and tracheal observation without the above-mentioned use, which is obviously advantageous. .

Recently, photographic laryngoscopes have removable, disposable blades to eliminate the need for sterilization.

A laryngoscope is a device that is used by a clinician during endotracheal intubation, particularly when it is directed through the glottis toward the trachea, to provide a clinician with a view of the cannula to assist intubation. Recently, the laryngoscope includes a handle and a blade, and often includes a light source. Some laryngoscopes also include viewing devices such as fiber optics and cameras. This type of phenomenon is called a photography throat mirror.

Most cannulas are straight and the clinician uses a laryngoscope with straight or curved leaves to place it in the patient's respiratory tract. However, it is known that some patients are difficult to intubate, especially if they have an anatomical deformity (for example if the throat is particularly placed first) or if there is a trauma. It would be more successful for such patients to intubate with differently shaped blades, such as the "difficult blades" detailed below. Preferably, the blade of the difficult cannula has a curved portion that smoothly follows the anatomical shape of the patient's trachea, a ventral-replaced distal portion extending to provide better visualization of the laryngeal inlet, and a wing. Guide the snorkel toward the throat inlet.

At this stage, there are no versatile blades for all patients, so there are some special blades that are needed and beneficial, so clinicians can use the selected blade shape to view the larynx inlet based on clinical needs, personal expertise and preferences. Because the existing camera laryngoscope must be used in conjunction with the matching blade shape, the user will use a completely different laryngoscope depending on the situation. For example, a clinician can insert a photographic laryngoscope into a patient using standard curved blades and be informed of the presence of a deformity based on the insertion, requiring a modified blade. He or she will then need a second photographic laryngoscope with a modified blade to view the throat inlet, which will increase the cost of the instrument for efficient operation. The blades are often disposable and relatively inexpensive, with the handle including an viewing device, which is typically expensive. Therefore, there is a need for a laryngoscope that can use different blade shapes.

It is an object of the present invention to eliminate problems such as those described above.

According to a first aspect of the present invention, there is provided a laryngoscope comprising a handle, a blade gripping member, a separable blade, and means for observing a patient's throat inlet, the laryngoscope further comprising means for adjusting the field of view.

Preferably, the laryngoscope configuration is used with at least two different separable blades, including, for example, straight blades, curved leaves, or blades designed especially for difficult intubators.

The blade may include a sleeve portion that completely or partially encloses the blade gripping member; and a distal end extension that is integrally formed with the sleeve portion. One-piece blades can be produced cheaply, and if used again, they are less polluting.

The detachable blade may further comprise means for guiding the cannula towards the distal end extension. This is especially helpful when clinicians face difficult and complicated intubation conditions.

In a preferred embodiment, the viewing means comprises at least one fixed camera device located at the distal end of the blade gripping member. Preferably, the means for adjusting the field of view comprises a means of photorefraction, such as a meander or a dovetail.

In other preferred embodiments, the viewing means includes at least two fixed camera units that point to two different fields of view. Preferably, the laryngoscope further comprises means for switching from the phase unit to the other; thus, for example, the first camera unit is adapted for use when the laryngoscope is used with a standard blade and the second camera unit is adapted for use when the blade is difficult to use Time.

In another embodiment, the viewing means comprises a movable camera unit. Preferably, the laryngoscope further comprises mechanical or electronic means for controlling the movement of the camera unit. For example, the distal end of the blade cannula portion includes a window that is provided such that when in use, the camera unit is positioned to view the patient's throat access.

According to a second aspect of the present invention, there is provided a method of viewing a patient's throat using a laryngoscope comprising a handle, a blade gripping member, a separable blade, and means for observing a patient's throat inlet, the method comprising adjusting the field of view A step of.

The invention will be described with the following figures and examples.

In the application of the present invention, the proper nouns "distal part" and "proximal part" are applied to the medical profession; for example, "tip site" is used to describe the first time. Insert a part of the device for the patient. The proper nouns "dorsal" and "ventral" are associated with a patient; for example, the "back" side is used to describe the side pointing to the patient's back, and the "abdominal" side It is used to describe the side that points to the front end of the patient.

Referring to Figures 1A through 1C, the laryngoscope (1) includes a handle (2) for holding and ingeniously operating the laryngoscope, a blade grip member (3) pivotally coupled to the handle (2), and a connection The detachable blade (4) of the blade grip element (3).

Although it can be made of other materials such as metal or plastic, the handle (2) is made of stainless steel for the sake of strength. At the proximal end, the blade grip element (3) is pivotally coupled to the root of the handle (2). Referring to Figures 1A through 1C, the vanes (4) are preferably hollow so that they are slidably mounted to the vane gripping elements (described in more detail below). Preferably, the blade gripping element (3) is elongate in shape and its outer shape generally corresponds to the inner shape of the blade (4).

The blade (4) is preferably integrally formed, for example by injection molding, so that the manufacturing cost is quite affordable. The blades are preferably disposable to reduce or eliminate the risk of cross-contamination between any patients. The blade may be partially or fully made of a transparent material to observe the area around the entrance to the throat.

The blade (4) can be straight (e.g., Miller laryngoscope blade) or curved (e.g., Macintosh blade). Curved leaves are often used by clinicians because curved leaves can be sized to accommodate bending of the patient's throat anatomy. Figure 2A shows a standard curved Macintosh blade (4a) comprising a sleeve (5a) configured to partially or completely enclose the blade grip element (3) having a proximal end and a distal end end. The distal end of the sleeve preferably includes a transparent window (6a). The blade (4a) further includes a distal end extension (7a) generally along the curvature of the blade (5a).

Fig. 2B shows a blade (4b) having an increased longitudinal condition. This type of blade (hereinafter also referred to as "difficult blade") facilitates the observation of the entrance to the larynx and is used for difficult and complicated cannulas.

The blade (4b) includes a sleeve (5b) configured to partially or completely enclose the blade grip element (3) having a proximal end and a distal end. The distal end of the sleeve preferably includes a transparent window (6b). The blade (4b) further includes a distal end extension (7b) that replaces the curvature of the blade (5b) on the abdomen side.

The difficult blade preferably includes guiding means for guiding the breathing tube into the correct position within the patient's respiratory tract. In the blade (4b) shown in Fig. 2B, the guiding device comprises a wing extending from the distal end of the sleeve (5b) and along the curvature of the sleeve to guide the tube towards the distal end extension (7b) top.

As mentioned above, the difficult blade (4b) is recommended for difficult and complicated cannulas, and the standard Macintosh blade (4a) is used for a relatively straight cannula. The standard blade (a) has a considerably cheaper advantage than the difficult blade (4b). In addition, the difficult blade (4b) can cause throat trauma when it is not necessary to use it in a simple case than a straight cannula. Therefore there will be a need to coexist both types of leaves, and the clinician will select the most appropriate blade for the situation.

The laryngoscope (1) further includes means for observing the entrance to the throat of the patient. The means can include a display screen (not shown), for example to view an area captured by the camera. A detachable or fixed display screen can be attached to the proximal end of the handle (2) or a separate display screen can be used. The advantage of using a detachable screen is that the device can be easily cleaned after use.

Preferably, the viewing means comprises at least one camera unit (9) which can be placed at the distal end of the blade grip element (3) so as to be directed towards the distal end of the blade (4). The images captured by the camera can be transmitted to the display screen and/or other means of visualization, such as by fiber optics.

The laryngoscope (1) may also include a light source and/or any other visual means that may externally indirectly observe the throat inlet. For example, a light source can be provided to illuminate the tip end of the blade.

During operation, the laryngoscope (1) is inserted into the patient's mouth. The blade (4) will push the patient's tongue to the oropharynx to create space for viewing the throat and epiglottis. The blade (4) is ingeniously operated to lift the epiglottis to expose the throat entrance.

A breathing tube can then be introduced and advanced through the vocal cord into the trachea. The snorkel can be inserted with the laryngoscope so that the snorkel and the laryngoscope are inserted and placed together at the same time. Alternatively, the laryngoscope is inserted first and the breathing tube is inserted when the laryngoscope is placed in the correct position. For example, through the display screen, the user can view the distal end of the blade and thus operate the laryngoscope (1) precisely. Once the breathing tube is properly placed, remove the laryngoscope (1).

The main problem solved by the present invention is to adjust the field of view. Therefore, under low distortion aberration and best focus, the clinician can clearly observe the patient's throat entrance regardless of which blade is placed on the blade holding member. Preferably, the field of view encompasses an observation angle of at least 30 degrees below the top end of the extension (7) for excellent throat entry observation. For example, when a difficult blade for a standard blade is used, it is not clearly visible because the field of view is obscured by the cannula guiding means and/or because the distal end of the blade is provided on the abdomen side.

First embodiment

3 shows a part of a laryngoscope according to a first embodiment of the invention; wherein the outer contour of the blade gripping element (3) substantially corresponds to a standard blade and a difficult blade (4a, 4b) sleeve (5a, 5b) The internal shape, so the blades can be used alternately for the same laryngoscope. A fixed camera unit (9) is located at the distal end of the blade grip element (3).

In Figures 4a and 5a, the blade gripping elements (3) are respectively associated with short standard curved blades and long standard curved blades (4a). The line HH passes through the center of the lens of the camera (9) and the pivotal joint of the handle (2) with the blade grip element (3). The camera (9) is set so that, on the plane defined by the line HH and the longitudinal axis of the handle (2), the center of the field of view captured by the camera is at an angle α ₁ , for example, from the line HH to a range of 5 to 15 degrees. In Figures 4a and 5a, the exemplary angle is 12.75 degrees and it has the smallest blade interference view.

The field of view captured by the camera (9) is shown in Figures 4b and 5b. The field of view is clear and undistorted (presented by a perfect square grid). These are satisfactory images, and ideally, the tip of the distal end extension (7a) should be visible so that the picture is accurately focused on the patient's throat entrance.

In Figure 6a, the blade grip element (3) fits over the difficult blade (4b). The distal end of the cannula (6b) includes a dovetail that changes the optical path so that, as shown in Figure 6b, the tip of the extension (7b) is visible to the patient's throat inlet. Preferably, by selecting 稜鏡, the center of view captured via the camera is located in an angular range, for example, 20 degrees to 40 degrees. In Figure 6b, the exemplary efficacy of 稜鏡 is 29 degrees, providing a model angle of 35.75 degrees (equivalent to the original angle α ₁ 12.75 degrees plus the abdominal side tilt angle β ₁ 23 degrees). However, the field of view captured by the camera (9) is slightly distorted by the compressed grid lines shown in Figure 6b.

In the first embodiment, the laryngoscope can use exchangeable blades. When the standard curved blade is placed, it is not necessary to use 稜鏡 because the camera position can be adjusted strategically to obtain a satisfactory view. As for difficult intubation, the clinician replaces the standard curved blade with a difficult blade and coordinates it to adjust the field of view as described above, thus providing a clear, undistorted view of the throat entrance.

Second embodiment

Figure 7 shows a portion of a laryngoscope in accordance with a second embodiment of the present invention. The main difference from the laryngoscope in Fig. 3 is the position of the camera (9). The camera (9) is set so that, on the plane defined by the line HH and the longitudinal axis of the handle (2), the center of the field of view captured by the camera is at an angle α ₂ , for example, from the line HH to a range of 15 to 25 degrees. The angle α _{2 is} greater than α ₁ (for example, 17 degrees).

In Figures 8a and 9a, the blade gripping elements are associated with short standard curved blades and long standard curved blades (4a), respectively. The field of view captured by the camera (9) is shown in Figures 8b and 9b and includes the top end of the extension (7a). The field of view is clear and undistorted (presented by a perfect square grid). These are satisfactory images that, when placed in a patient, are precisely focused on the patient's throat entrance.

In Figure 10a, the blade grip element (3) is used in conjunction with the difficult blade (4b). The distal end of the sleeve (6b) includes a dovetail that changes the optical path so that, as shown in Figure 10b, the top end of the extension (7b) is visible. Preferably, by selecting 稜鏡, the center of view captured via the camera is located in an angular range, for example, 30 degrees to 45 degrees. In Figure 6b, the exemplary efficacy of 稜鏡 is 25 degrees, providing a typical angle of 37 degrees (equivalent to the original angle α ₂ 17 degrees plus the abdomen side tilt angle β ₂ 20 degrees). The field of view captured by the camera (9) is less distorted and clearer than the image obtained by the stronger potent wedge of the first embodiment.

Third embodiment

Figure 11 shows a portion of a laryngoscope in accordance with a third embodiment of the present invention. The camera (9) is set so that, on the plane defined by the line HH and the longitudinal axis of the handle (2), the center of the field of view captured by the camera is at an angle α ₃ , for example, from the line HH to a range of 25 to 40 degrees. The angle α _{3 is} larger than α ₁ and α ₂ (for example, 32 degrees).

In Figures 12a and 13a, the blade gripping elements (3) are associated with short standard curved blades and long standard curved blades (4a), respectively. Further, a dovetail is mounted on the distal end of the sleeve (6a) to guide the field of view toward the top end of the extension.

Figures 12b and 13b show the use of the blades of Figures 12a and 13a and the change of the camera position (without wedges). No distortion is observed and the field of view is clear. However, the extension (7a) will obscure (nearly 1/3) the field of view.

In contrast, when a dovetail is placed on the blade (as in Figures 12c and 13c), the top end of the extension is visible and does not substantially obstruct the view. A slight distortion can be observed, but the field of view is quite clear and the patient's respiratory tract can be examined for efficient insertion of the catheter. In Figures 12a and 13a, the exemplary effectiveness of 稜鏡 is 20 degrees, providing a model angle of 18 degrees, which is equivalent to the original angle α ₃ 32 degrees minus the back side tilt angle β ₃ 14 degrees. In this example, since the Prism provided, so subtracted from the original angle of inclination angle α ₃ β _3, and therefore a back side of the readjustment vision, rather than (as shown in the foregoing embodiment) to the ventral side.

In Figure 14a, the blade grip element (3) is used with the difficult blade (4b). The exemplary effectiveness of 稜鏡 is 20 degrees, and a typical angle of 46 degrees can be provided, which is equivalent to the original angle α ₃ 32 degrees of setting the camera plus the angle of inclination of the abdominal side β ₃ 14 degrees due to the use of 稜鏡. As shown in Figure 14c, a clear field of view that significantly reduces distortion can be obtained.

In contrast, Figure 14b shows the field of view obtained using the blade of Figure 14a and repositioning the camera (without wedges). No distortion is observed and the field of view is clear, but the top end of the extension (7b) is not visible, ie the field of view is precisely focused on the patient's throat entrance.

Fourth embodiment

The laryngoscope of Fig. 15 is similar to that shown in Fig. 11. The difference lies in the setting of the camera (9), so that on the plane defined by the line HH and the longitudinal axis of the handle (2), the center of the field of view captured by the camera is developed at an angle α ₄ , for example, from the line HH to 27.5 degrees.

In Figures 16a and 17a, the blade gripping elements (3) are associated with short standard curved blades and long standard curved blades (4a), respectively. The dovetail is weaker than the third embodiment, for example, has an effect of 16 degrees and results in an angle of 18 degrees, which is equivalent to the original angle α ₄ 27.5 degrees due to the position of the camera minus the back side tilt angle β _{4 of} 9.5 degrees due to the presence of 稜鏡.

As shown in Figures 16b and 17b, when the blade (4a) is not used with a dovetail, the extension (7a) obscures the field of view, but the field of view is clear and undistorted. When the iliac crest is placed at the distal end of the cannula (5a) of the blade (4a), only the tip of the extension (7a) is visible, thereby showing that the treatment must be done to obtain a focused view of the larynx entrance (see Figure 16c and Figure 17c). Only a little distorted and clear vision.

In Figure 18a, the blade grip element (3) is used in conjunction with the difficult blade (4b). The exemplary effectiveness of 稜鏡 is 21.5 degrees, providing a model angle of 35.75 degrees, which is quite due to the original angle of the camera position α ₄ 27.5 degrees plus the abdominal side tilt angle β ₄ 17.5 degrees due to the use of 稜鏡. As shown in Figure 18c, a clear field of view that significantly reduces distortion can be obtained.

In contrast, Figure 18b shows the field of view obtained using the blade of Figure 18a and repositioning the camera (without wedges). No distortion is observed and the field of view is clear, but the top end of the extension (7b) is not visible.

Fifth embodiment

The blade grip element (3) is used in conjunction with at least a first camera and a second camera (9). When a standard blade is used and the first camera is set, a clear, undistorted view of the throat is obtained for the throat inlet; when the difficult blade is used and the second camera is set, a clear, undistorted view of the throat is obtained. The laryngoscope is used with observations to allow the clinician to use a laryngoscope with at least one standard and difficult blade to limit the cost of the expenditure. In addition, such laryngoscopes can use blades that do not require sputum or any other means of adjusting the field of view because the field of view has been adjusted using a multi-camera system.

The laryngoscope (1) may further comprise switching means (e.g. electronic means) for switching from one camera to another so that the clinician may choose to use the first and/or second camera depending on the desired field of view, and with the blade The type of blade that holds the component.

Sixth embodiment

The present invention further changes the laryngoscope of the fifth embodiment in place of a multi-camera system by using a single movable or "tiltable" camera (9) in conjunction with the distal end of the blade gripping member (3). For example, the camera can be packaged in a low-friction housing that can tilt the camera with a mechanism or electronic means so that the field of view is focused on the patient's throat portal. Such a laryngoscope can be used with the blade and does not require any flaws or any other means of adjusting the field of view.

The laryngoscope (1) may further comprise means for positioning the camera in a desired position, thereby obtaining a clear, undistorted view of the throat entrance. For example, the laryngoscope can include mechanical or electronic means to remotely change the position of the camera. Alternatively, the blade automatically adjusts the position of the camera when the blade is gripped with the blade. For example, the distal end (6) of the cannula (5) can be constructed or molded at an angle so that with the blade of the blade gripping element, the distal end or window (6) pushes the camera to a suitable position for clarity The top end of the blade extension (7) is observed in a twisted form. Such a structure is shown in Fig. 20a, Fig. 21a, and Fig. 22a, and the corresponding fields of view are shown in Fig. 20b, Fig. 21b, and Fig. 22b.

When the blade includes a dovetail, the file can be mated to the blade by any suitable means, including, for example, screws and/or glue. Preferably, the crucible is integrally molded to the distal end of the sleeve. The integrally provided crucible has the advantage of being cheaper, stronger and less prone to contamination.

It is believed that more than 95% of intubations can now be performed using standard vanes, and for the remaining 5% (or less) of cannulas, clinicians need to purchase laryngoscopes that are specifically designed for use with difficult blades. The laryngoscope described above allows the clinician to reduce the cost of the expenditure, since only one versatile laryngoscope is needed for physiologically and functionally distinct blades. In addition, different types of leaves can be used alternately without a clear view of the throat entrance of the patient.

While the present invention has been described in its preferred embodiments, the present invention is not intended to limit the invention, and the present invention may be modified and modified without departing from the spirit and scope of the invention. The scope of protection is subject to the definition of the scope of the patent application.

1‧‧‧ throat mirror

2‧‧‧Hands

3‧‧‧blade holding components

4‧‧‧ separable blades

4a‧‧‧ leaves

5a‧‧‧ casing

6a‧‧‧Window

7a‧‧‧ distal end extension

4b‧‧‧difficult blades

9‧‧‧Photo unit

1A to 1C show a laryngoscope according to the present invention; Figure 2A shows a standard curved blade; Figure 2B shows the blade for a difficult cannula; Figure 3 is a view showing a portion of a laryngoscope according to a first embodiment of the present invention; Figure 4a shows the laryngoscope of Figure 3 with a standard short curved blade; Figure 4b shows the field of view obtained from the laryngoscope of Figure 4a; Figure 5a shows the laryngoscope of Figure 3 with a standard long curved blade; Figure 5b shows the field of view obtained from the laryngoscope of Figure 5a; Figure 6a shows that the laryngoscope of Figure 3 is equipped with a difficult blade; Figure 6b shows the field of view obtained from the laryngoscope of Figure 6a; Figure 7 is a view showing a portion of a laryngoscope according to a second embodiment of the present invention; Figure 8a shows the laryngoscope of Figure 7 with a standard short curved blade; Figure 8b shows the field of view obtained from the laryngoscope of Figure 8a; Figure 9a shows the laryngoscope of Figure 7 with a standard long curved blade; Figure 9b shows the field of view obtained from the laryngoscope of Figure 9a; Figure 10a shows the throat mirror device of Figure 7 with a difficult blade; Figure 10b shows the field of view obtained from the laryngoscope of Figure 10a; Figure 11 is a view showing a portion of a laryngoscope according to a third embodiment of the present invention; Figure 12a shows the laryngoscope of Figure 11 with a standard short curved blade; Figure 12b shows the field of view obtained from the laryngoscope of Figure 12a without using 稜鏡; Figure 12c shows the field of view obtained from the laryngoscope of Figure 12a using 稜鏡; Figure 13a shows the laryngoscope of Figure 11 with a standard short curved blade; Figure 13b shows the field of view obtained from the laryngoscope of Figure 13a without the use of 稜鏡; Figure 13c shows the use of 稜鏡, shown from the 12th Figure 14a shows the laryngoscope of Figure 11 with a standard short curved blade; Figure 14b shows the field of view obtained from the laryngoscope of Figure 14a without the use of 稜鏡; Figure 14c is used稜鏡, showing the field of view obtained from the laryngoscope of Fig. 14a; Fig. 15 shows a part of the laryngoscope according to the fourth embodiment of the invention; Fig. 16a shows the laryngoscope of Fig. 15 with a standard short curved blade Figure 16b shows no view of the field of view obtained from the laryngoscope of Figure 16a; Figure 16c shows the field of view obtained from the laryngoscope of Figure 16a; Figure 17a shows the laryngoscope of Figure 15 A standard short curved blade is installed; Figure 17b shows the unused field of view, showing the field of view obtained from the laryngoscope of Figure 17a; Figure 17c uses 稜鏡 to display the field of view obtained from the laryngoscope of Figure 17a; Figure 18a shows the laryngoscope of Figure 15 with a standard short curved blade; Figure 18b shows the unused 稜鏡, shown from the 18a Figure 18c shows the field of view obtained from the laryngoscope of Figure 18a using 稜鏡; Figure 19 shows a part of the laryngoscope according to the sixth embodiment of the invention; Figure 20a shows the Figure 19 shows the laryngoscope with a standard short curved blade; Figure 20b shows the field of view obtained from the laryngoscope of Figure 20a; Figure 21a shows the laryngoscope of Figure 19 with a standard long curved blade; Figure 21b The field of view obtained from the laryngoscope of Fig. 20a is shown; Fig. 22a shows that the laryngoscope of Fig. 19 is equipped with a difficult blade; and Fig. 22b shows the field of view obtained from the laryngoscope of Fig. 20a.

1. . . Throat mirror

2. . . handle

3. . . Blade holding element

4. . . blade

9. . . Camera unit

Claims (13)

A laryngoscope comprising: a handle; an elongated blade gripping member comprising: one viewing device for viewing a patient's throat inlet; and at least two different separable blades, at least one of which includes Adjusting an adjustment element of a field of view of the viewing device to observe the patient's throat inlet such that a tip of a distal end extension of at least one of the blades is viewable by the viewing device to observe the disease Suffering from the throat entrance. The laryngoscope of claim 1, wherein the blade comprises a sleeve portion. A laryngoscope according to claim 3, wherein the blade further comprises a wing for guiding a breathing tube to move toward a tip end of the distal end extension. The laryngoscope according to any one of claims 1 to 3, wherein the viewing device comprises at least one fixed camera unit disposed at a distal end of the blade gripping member. The laryngoscope of claim 4, wherein the adjustment element that adjusts the field of view comprises a light-refracting element. The laryngoscope of claim 5, wherein the light-refracting element further comprises a dove or a dovetail. The laryngoscope of claim 1, wherein the viewing device comprises at least two fixed camera units that point to two different views wild. The laryngoscope of claim 7, wherein the image received by the laryngoscope is switchable from one of the camera units to another camera unit. The laryngoscope of claim 2, wherein the viewing device comprises a movable camera unit. The laryngoscope of claim 9, wherein the distal end of the cannula portion of the blade includes a window such that, in use, the movable camera unit is positioned to view a patient's throat inlet. A method of operating a laryngoscope as described in claim 1 for observing a throat entrance of a patient, comprising: evaluating the patient, determining whether the patient has a physiological structural abnormality or injury and using the blade If necessary, the blade is attached to the blade grip element to achieve the desired viewing angle. The method of claim 11, wherein the viewing device comprises at least two camera units, and the field of view is adjusted by switching from one of the camera units to the other. The method of claim 11, wherein the field of view is adjusted by moving the camera unit.